Models for Bimetallic Catalysis: Selectivity in Ligand Addition to a

Brian T. Sterenberg, Michael C. Jennings, and Richard J. Puddephatt ... Leijun Hao, Jianliang Xiao, Jagadese J. Vittal, and Richard J. Puddephatt...
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Organometallics 1995, 14, 4183-4193

4183

Models for Bimetallic Catalysis: Selectivity in Ligand Addition to a Coordinatively Unsaturated PtsRe Cluster Cation Jianliang Xiao, Leijun Hao, and Richard J. Puddephatt" Department of Chemistry, University of Western Ontario, London, Canada N 6 A 5B7

Ljubica Manojlovik-Muir," Kenneth W. Muir, and Ali Ashgar Torabi Department of Chemistry, University of Glasgow, Glasgow, Scotland G12 SQQ Received April 19, 1995@ The coordinatively unsaturated, 54-electron Pt3Re cluster cation [Pt3{Re(C0)3}@-dppm)31+, 2, dppm = Ph2PCH2PPh2, reacts with ligands L = P(OR)3, CO, RNC, RSH or RC=CH to give the 56-electron cluster cations [Pta{Re(C0)3L}@-dppm)31+by selective addition to the rhenium center, in contrast to the known addition of these ligands to the Pt3 center in [Pt3@3CO)(p-dppm)3I2+. The reaction with CO is easily reversible. The complex with L = P(OPh)3 has been characterized by a n X-ray structure determination { [Pt3{Re(C0)3L}@-dppm)31[PF6+EtOH; triclinic, Pi, a = 13.993(1) 8, b = 17.868(1) 8,c = 19.753(2)A, a = 88.198(7)", ,4 = 87.766(7)", y = 72.394(4)", V = 4702.9(7) Hi3, Z = 2, R = 0.0405, R, = 0.0429 for 14 765 unique reflections with I > 3a(I)}. The structure contains a distorted tetrahedral PtsRe core with the Pt3 triangle edge-bridged by three p-dppm ligands, the two PtRe edges weakly semibrid ed by CO ligands, and the phosphite ligand bound to rhenium [Pt-Pt = 2.603(1)2.677(1) , Pt-Re = 2.762(1)-2.942(1) 81. NMR studies indicate that several of the adducts are fluxional, by rotation of the Re(C0)3L fragment about the Pt3 triangle, such that they appear t o have C3 symmetry. Phosphite ligands displace CO or HCCH from [Pts{Re(CO)r}@ - d ~ p m ) ~or] +[Pt3{Re(CO)3(HCCH)}@-dppm)#, respectively, to give [Pt3{Re(C0)3P(OR)3}(p-dppm)s]'. The clusters are considered to be formed by donation of electron pairs from the Pt-Pt bonding orbitals of a Pt3@-dppm)3fragment to acceptor orbitals of the Re(C0)3 or Re(C0)sL unit; Pt-Re bonding is therefore weaker in the 56-electron clusters. An analogy is noted between the donor orbitals of the Pts@-dppm)s fragment and of C5H5-, which is useful in interpreting the chemistry. The observation of selective reactivity a t rhenium is relevant to the mode of action of heterogeneous Pt/Re catalysts.

1

Introduction Heteronuclear transition metal cluster complexes have fascinating properties and are of particular interest as models for heterogeneous bimetallic alloy catalysts.1,2 One of the most important of such catalysts is the Pt/Re/AlzO3 system used in catalytic reforming of p e t r ~ l e u m . As ~ a result of this interest, several binuclear and cluster complexes containing Pt-Re bonds have been synthesized and structurally characterized and can serve as models for the metal-metal-bonded units which may be present in the bimetallic catalyst^.^ However, there have been few studies of the chemical ~ , ~ to reactivity of Pt-Re-bonded c ~ m p l e x e s . ~In~order model the reactivity of a bimetallic catalyst compared to a simple platinum catalyst, it would be useful to study the reactivity of a coordinatively unsaturated Pt-Re cluster compared to a simple Pt cluster. This is now @Abstractpublished in Advance ACS Abstracts, August 1, 1995. (1)(a)Adams, R.D.; Wu, W. Organometallics 1993,12,1238;1248. (b) Churchill, M. R.; Lake, C. H.; Safarowic, F. J.; Parfitt, D. S.; Nevinger, L. R.; Keister, J. B. Organometallics 1993,12,671. ( c ) Song, L. C.; Shen, J. Y.; Hu, Q.M.; Wang, R. J.;Wang, H. G. Organometallics 1993, 12, 408. (d) Adams, R. D.; Li, Z.; Swepston, P.; Wu, W.; Yamamoto, J. J . Am. Chem. SOC.1992,114,10657.( e ) Farrugia, L. J. Adv. Organomet. Chem. 1990,31,301. (2)Adams, R.D.; Herrmann, W. A. Polyhedron 1988,7,2255-2464. (3)Biswas, J.;Bickle, G. M.; Gray, P. G.; Do, D. D.; Barbier, J. Catal. Rev. Sci. Eng. 1988,30, 161.

possible with clusters based on the Ptaf&-dppm)striangle, dppm = PhzPCHzPPh2, since both cluster cations [Pt3f&3-CO)f&-dppm)3I2+, 1,6 and [Pt3{p3-Re(C0)31010

1

2, M=Re; 3, M = M n

dppm)3]+,2,5 are now known. The complex cations 1 and 2 have 42- and 54-electron configurations, respec(4) (a) Xiao, J.;Vittal, J. J.; Puddephatt, R. J. J . Chem. SOC.,Chem. Commun. 1993, 167. (b) Beringhelli, T.;Ceriotti, A.; Ciani, G.; D'Alfonso, G.; Garlaschelli, L.; Pergola, R. D.; Moret, M.; Sironi, A. J . Chem. SOC.,Dalton Trans. 1993,199.( c ) Antognazza, P.; Beringhelli, T.; DAlfonso, G.; Minoja, A,; Ciani, G.; Moret, M.; Sironi,A. Organometallics 1992,11,1777.(d) Powell, J.;Brewer, J. C.; Gulia, G.; Sawyer, J. F. J. Chem. SOC.,Dalton Trans. 1992, 2503. (e) Beringhelli, T.; DAlfonso, G.; Minoja, A. P. Organometallics 1991,10,394.(0 Ciani, G.; Moret, M.; Sironi, A,; Antognazza, P.; Beringhelli, T.; D'Alfonso, G.; Pergola, R. D.; Minoja, A. J . Chem. SOC.,Chem. Commun. 1991, 1255.(g) Ciani, G.; Moret, M.; Sironi, A,; Beringhelli, T.; D'Alfonso, G.; Pergola, R. D. J. Chem. SOC.,Chem. Commun. 1990, 1668.(h) Beringhelli, T.; Ceriotti, A,; D'Alfonso, G.; Pergola, R. D. Organometallics 1990,9,1053.(i) Carr, S. W.; Fontaine, X. L. R.; Shaw, B. L.; Thornton-Pett,M. J . Chem. SOC.,Dalton Trans. 1988,769.

0276-7333/95/2314-4183~09.~0l00 1995 American Chemical Society

Xiao et al.

4184 Organometallics, Vol. 14, No. 9, 1995 tively, and so each is coordinatively unsaturated (the common electron counts for trinuclear and tetranuclear clusters are 48 and 60, re~pectively).~ In heteronuclear clusters containing platinum, the coordinative unsaturation is normally localized at the platinum, which commonly has a 16-electron configuration in mononuclear, binuclear, and cluster c~mplexes.~ Of course, the complex cation 1 can only react a t platinum, but previous work on mixed platinudmain group metal clusters, such as those containing Pt3(L43-SnX3)or Pt3h3Hg) units, has shown that ligands add selectively to platinum as expected, sometimes with displacement of the main group meta1.8,9 It is therefore particularly interesting that neutral donor ligands react with complex 2 at rhenium and not at one or more of the platinum centers,1° while anionic ligands such as I- add to the Pt3 triangle.'l This article reports details of the neutral ligand addition reactions to 2 and, to a lesser extent, to the corresponding manganese cluster [Pt3@3Mn(C0)3)(L4-dppm)31+,3,using the reagents CO, RNC, P(OR)3, RSH, and RCECH. Previous communications have reported the synthesis of 2 and 3 and the unique reactions of 2 with oxygen and sulfur donor^.^

Results

It will be seen that the ligand addition reactions are much better defined with the rhenium cluster 2 than with the manganese analog 3. The reactions with phosphite ligands, carbon monoxide, and alkynes will be described in that order. Reactions with Phosphite Ligands. Phosphite ligands reacted rapidly with cluster 2 to give the adducts [Pt3(Re(C0)3L}@-dppm)31+,[4, L = P(OMe)3; 5, L = P(OPh)3] according to eq 1. These complexes, as the 0

l +

i o0 z.

/

OC-Re-CO

1'

[PF& salts, are dark brown solids; they are stable to (5) (a)Xiao, J.;Vitpal, J. J.; Puddephatt, R. J.; ManojloviC-Muir, Lj.; Muir, K. W. J . A m . Chem. Soc. 1993,115,7882.(b) Hao, L.; Xiao, J.; Vittal, J. J.; Puddephatt, R. J. J. Chem. SOC.,Chem. Commun. 1994,

2183. (6)Ferguson, G.;Lloyd, B. R.; Puddephatt, R. J. Organometallics 1986,5,344.

air at room temperature, and they do not easily undergo ligand dissociation of either a carbonyl or the phosphite ligand. It is important to note that 1 reacts with these ligands in a completely different way, namely by addition to platinum as shown in eq 2.8J2 .#

ti

12+

1

0 /I

1*+

Complex 5 was characterized by an X-ray structure analysis of 5[PFsl'EtOH. Selected bond lengths and angles are listed in Table 1. The molecular structure of 5, presented in Figure 1, shows that addition of the phosphite ligand to 2 occurs selectively at the rhenium center. The structure is built of Re(C0)3{P(OPh)3}+ and Pt&-dppm)s fragments. The Pt3 triangle is capped by the Re(C0)3{P(OPh)3}+fragment to form a distorted tetrahedral Pt3Re cluster with two edges, Pt(l)-Re and Pt(2)-Re, weakly semibridged by carbonyl ligands [ReC = 1.969(9), 1.998(9)A; Pt-C = 2.428(9), 2.550(9) A; Re-C-0 = 171.4(8), 170.6(8)"1. The Pt3Re(C0)3(P03)@-PCP)3 core approximates C, symmetry (Figure 21, with the mirror plane passing through the Pt(3), Re, P(7), C(1), and C(4) atoms and bisecting the Pt(l)-Pt(2) bond. Distorted octahedral geometry about the Re atom in the Re(C0)3{P(OPh)3}+unit, evident from the bond angles shown in Table 1, is completed by the Pt(3) atom and the midpoint of the Pt(l)-Pt(2) bond. In 5, the Pt-Pt bonds show small variations [2.603(1), 2.635(1),2.677(1)AI. Variations in the Pt-Re distances are larger [2.762(1),2.825(1), 2.942(1)AI, but all three distances lie within the accepted range of 2.65-3.00 A.4,5,10J1 The average Pt-Pt (2.60 A in 2, 2.64 A in 5 ) and Pt-Re (2.67 A in 2, 2.84 A in 5 ) distances indicate that the phosphite addition occurs at the expense of metal-metal bonding, with the Pt-Re bonds weakened more than the Pt-Pt bonds. (7)Mingos, D. M. P.; May, A. S.In The Chemistry of Metal Cluster Complexes: Shriver, D. F., Kaesz, H. D., Adams, R. D., Eds.; VCH: New York, 1990. The most common electron count for tetrahedral clusters is 60,such as in [IrdC0)1~1. (8)Puddephatt, R. J.; ManojloviC-Muir, Lj.; Muir, K. W. Polyhedron 1990,9, 2767. (9)(a) Jennings, M. C.; Schoettel, G.; Roy, S.; Puddephatt, R. J.; Douglas, G.; ManojloviC-Muir, Lj.; Muir, K. W. Organometallics 1991, 10,580.(b) Schoettel, G.;Vittal, J. J.; Puddephatt, R. J. J . Am. Chem. SOC.1990,112,6400.(c) Payne, N. C.; Ramachandran, R.; Schoettel, G.; Vittal, J. J.; Puddephatt, R. J. Inorg. Chem. 1991,30, 4048. (10)Xiao, J.; Hao, L.; Puddephatt, R. J.; ManojloviC-Muir, Lj.; Muir, K. W.; Torabi, A. A. J. Chem. SOC.,Chem. Commun. 1994,2221. (11) Xiao, J.; Hao, L.; Puddephatt, R. J.; ManojloviC-Muir, Lj.; Muir, K. W.; Torabi, A. A. Organometallics, 1995,1 4 , 2194. (12)(a) Bradford, A. M.; Douglas, G.; ManojloviC-Muir, Lj.; Muir, K. W.; Puddephatt, R. J. Organometallics 1990,9, 409.(b) Bradford, A. M.; Kristof, E.; Rashidi, M.; Yang, D.-S.; Payne, N. C.; Puddephatt, R. J. Inorg. Chem. 1994,33,2355.(c) Jennings, M. C.; Payne, N. C.; Puddephatt, R. J. Inorg. Chem. 1987,26,3776.

Organometallics, Vol. 14,No. 9,1995 4185

Models for Bimetallic Catalysis Table 1. Selected Interatomic Distances Pt(1)-Pt(2) Pt(1)-Re Pt(l)-P(B) Pt(2)-Pt(3) Pt(2)-P(1) Pt(2)-C(5) Pt(3)-P(3) Re-P(7) Re-C(5) Pt(2)-Pt(l)-Pt(3) Pt(2)-Pt(l)-P(2) Pt(S)-Pt(l)-C(G) Pt(3)-Pt( 1)-P(2) Pt(3)-Pt(l)-C(6) Re-Pt( 1)-P(5) P(2)-Pt(l)-P(5) P(5)-Pt(l)-C(6) Pt(l)-Pt(2)-Re Pt(l)-Pt(2)-P(4) Pt(B)-Pt(2)-Re Pt(3)-Pt(2)-P(4) Re-Pt(Z)-P(l) Re-Pt(2)-C(5) P(l)-Pt(2)-C(5) Pt(l)-Pt(3)-Pt(2) Pt(l)-Pt(3)-P(3) Pt(2)-Pt(3)-Re P5(2)-Pt(3)-P(6) Re-Pt(3)-P(G) Pt(l)-Re-Pt(2) Pt(l)-Re-P(7) Pt(l)-Re-C(5) Pt(2)-Re-Pt(3 ) Pt(2)-Re-C(4) Pt(2)-Re-C(6) Pt(3)-Re-C(4) Pt(3)-Re-C(6) P(7)-Re-C(5)

2.677(1) 2.825(1) 2.253(3) 2.603(1) 2.268(3) 2.428(9) 2.307(2) 2.255(3) 1.998(9) 58.7(1) 96.6(1) 102.7(2) 155.1(1) 88.1(2) 132.2(1) 108.6(1) 99.4(3) 62.6(1) 139.0(1) 66.4(1) 92.0(1) 109.7(1) 44.7(3) 113.5(3) 61.5(1) 155.1(1) 59.4(1) 155.6(1) 115.6(1) 57.2(1) 126.6(1) 115.6(3) 54.2(1) 136.0(3) 118.4(3) 94.9(3) 92.3(3) 94.5(3)

Pt(l)-Pt(3) Pt(l)-P(Q) Pt(l)-C(6) Pt(2)-Re Pt(2)-P(4) Pt(3)-Re Pt(3)-P(6) Re-C(4) Re-C(6) Pt(2)-Pt(l)-Re Pt(2)-Pt(l)-P(5) Pt(S)-Pt(l)-Re Pt(3)-Pt(l)-P(5) Re -Pt(1)- P(2) Re-Pt(l)-C(G) P(2)-Pt(l)-C(6) Pt(l)-Pt(2)-Pt(3) Pt(l)-Pt(2)-P(l) Pt(l)-Pt(2)-C(5) Pt(3)-Pt(2)-P(l) Pt(3)-Pt(2)-C(5) Re-Pt(2)-P(4) P(l)-Pt(2)-P(4) P(4)-Pt(2)-C(5) Pt(l)-Pt(3)-Re Pt(l)-Pt(S)-P(G) Pt(2)-Pt(3)-P(3) Re-Pt(3)-P(3) P(3)-Pt(3)-P(6) Pt(l)-Re-Pt(3) Pt(l)-Re-C(4) Pt(l)-Re-C(6) Pt(2)-Re-P(7) Pt(2)-Re-C(5) Pt(3)-Re-P(7) Pt(3)-Re-C(5) P(7)-Re-C(4) P(7)-Re-C(6)

(A) and Angles (deg)

2.635(1) 2.298(2) 2.550(9) 2.762(1) 2.289(3) 2.942( 1) 2.281(3) 1.885(10)

1.969(9) 60.2(1) 142.0(1) 65.1(1) 91.9(1) 107.3(1) 42.6(2) 101.8(3) 59.8(1) 93.5(1) 107.0(3) 152.3(1) 83.6(3) 136.3(1) 106.1(1) 97.8(3) 60.6(1) 94.8(1) 93.8(1) 110.2(1) 109.6(1) 54.3(1) 133.2(3) 61.2(3) 124.0(1) 58.7(3) 177.6(1) 83.2(3) 85.8(3) 90.0(3)

C(4)-Re-C(5) C(5)-Re-C(6) Pt(2)-P(l)-C(El) C(l)-P( 1)-C(E 1) C(El)-P(l)-C(Fl) Pt(l)-P(2)-C(Cl) C(l)-P(B)-C(Cl) C(Cl)-P(B)-C(Dl) Pt(3)-P(3)-C(Kl) C(2)-P(3)-C(Kl) C(Kl)-P(S)-C(Ml) Pt(2)-P(4)-C(Jl) C(2)-P(4)-C(Jl) C(Jl)-P(4)-C(Ll) Pt(l)-P(5)-C(Nl) C(3)-P(5)-C(Nl) C(Nl)-P(5)-C(Ol) Pt(B)-P(6)-C(Al) C(3)-P(6)-C(Al) C(Al)-P(G)-C(Bl) Re -P(7)-O(2) 0(1)-P(7)-0(2) P(2)-P(7)-0(3) P(7)-0(2)-C(Hl) P(l)-C(l)-P(2) P(5)-C(3)-P(6) Pt(2)-C(5)-Re Re-C(5)-0(5) Pt(l)-C(6)-0(6)

90.5(4) 175.5(4) 111.7(4) 106.7(5) 106.6(5) 122.2(3) 101.9(4) 102.8(5) 118.1(4) 104.5(5) 101.4(4) 115.6(4) 103.0(4) 105.2(5) 119.4(4) 103.7(4) 102.2(5) 120.8(4) 101.6(5) 105.7(4) 120.1(3) 98.4(4) 95.9(3) 126.3(5) 112.2(4) 108.2(4) 76.5(3) 171.4(8) 112.9(6)

89.9(4) 111.1(3) 121.0(3) 98.2(5) 108.8(3) 115.7(3) 103.2(4) 113.5(3) 115.9(3) 101.2(4) 109.1(3) 120.0(4) 101.7(4) 108.0(3) 118.7(4) 102.8(4) 112.2(3) 113.1(3) 101.3(4) 113.9(3) 122.4(3) 101.9(3) 129.9(6) 123.9(6) 111.4(4) 178.1(9) 111.9(6) 76.2(3) 170.6(8)

Figure 2. View of the inner core of 5, using 50% probability ellipsoids. Only the ipso carbon atoms of the phenyl groups are shown. U

Figure 1. View of the molecular structure of 6,with atoms represented by spheres of arbitrary size. In the phenyl rings, atoms are numbered in sequences C(n1)...C(n6), where n = A - L and the C(n1) atom is P- or 0-bonded. The H atoms are omitted for clarity.

In the Pt&-dppm)s fragment, the RSP6 skeleton is severely distorted from the ideal latitudinal geometry (Figure 2). All Pt-P bonds are bent out of the P t 3 plane

and away from the bulky Re(C0)3{P(OPh)3}+fragment. The out-of-plane dis lacement of the phosphorus atoms [0.088(2)-1.195(2) i l3 is particularly large for the P(4) and P(5) atoms [1.195(2) and 0.969(2) AI, evidently to create space for the semibridging carbonyl ligands. The conformation of the Pt3P6C3 unit differs from that in 2, where the Pt3P6 skeleton is essentially planar and all three Pt2PzC rings show envelope conformations with carbon a t the flap.5 In 6 the three rings also adopt

Xiao et al.

4186 Organometallics, Vol. 14, No. 9, 1995

:/ oc--Fie-co 2

25°C

do

-

2

+

/I\

NMR labeling for 3 8

n

-80°C

different couplings %I(PtP) were observed. Thus the resonance was interpreted as a 1:4:1 triplet [due to coupling to one platinum atom with 2J(Pt2P)= 300 Hzl of 1:8:18:8:1 quintets [due to coupling to two equivalent platinum atoms with 2J(Pt1P)= 135 HzI.lo The average x 135 300) coupling is therefore expected to be = 190 Hz, in good agreement with the observed value of 194 Hz. The mechanism of fluxionality is proposed to be that shown in eq 3. It involves rotation of the

+

I ~ ' " I ' ' ~ '

118

126

'

~

"

~

~

114

'

~

"

'

~

112

~

~

~

~

~

i10

~

'

l

~

"

"

'

"

108 PPW

Figure 3. 31PNMR spectra of complex 5 in the region of the P(OPh)3ligand. Upper, spectrum at 25 "C showing the apparent 1:4:7:4:1 quintet due to equal coupling to all platinum atoms in the fast fluxionality region. Lower, spectrum at -80 "C showing the 1:4:1triplet of 1:8:18:8:1 quintets due to coupling to Pt2 and 2 x Ptl, respectively, in the slow rotation region. envelope conformations,but with carbon at the flap only in the Pt(l)Pt(2)P(l)C(l)P(2)ring; in the other two rings the flaps are occupied by phosphorus atoms, P(4) and P(5) (Figure 2). The spectroscopic data give further insight into the nature of the cluster cations 4 and 5. The IR spectra of both 4 and 5 displayed three bands due to terminal carbonyls, as expected for the structure of Figure 1.The stretching frequencies were decreased slightly compared to 2,5indicating that the phosphites are net donors to rhenium. The room temperature 31P NMR spectra contained a singlet resonance due to the dppm phosphorus atoms and a 1:4:7:4:1 quintet for the phosphite ligand. The quintet resonance is characteristic of a nucleus with equal coupling to three platinum atoms and, together with the singlet dppm resonance, suggests that the clusters have C3 symmetry on the NMR time scale.*-1° Since the actual symmetry is lower (Figure 11,the clusters must be fluxional. The average coupling between platinum and the phosphite phosphorus, J(PtP), is 157 and 194 Hz for 4 and 5, respectively. Such small but are consiscouplings cannot be due t o 1J(PtP)B,8-10 tent with a longer range V(PtReP) coupling, as expected if P(OR)3 adds to the rhenium atom of 2. The apparent fluxionality of 4 and 5 was studied by low-temperature 31PNMR spectroscopy. At -80 "C, the singlet dppm phosphorus resonance observed a t room temperature for 5 split to give three resolved resonances. This is expected for the structure shown in eq 1,which possesses a plane of symmetry containing the atoms LRe(C10)Pt2 (note that the atom labeling is different from that in Figure 1). Analysis of the resonance due to the phosphite ligand of 5 was also informative. At ambient temperature, this resonance appeared as a 1:4:7:4:1 quintet with V(PtP) = 194 Hz (Figure 3). At -80 "C, this signal was broader and two

"

~

~

"

~

"

~

~

~

~

~

"

1

+

__L

L

0

C

+

-

Re(C0)3L unit about the P t 3 triangle, with each stable structure having an approximately linear L-Re-Pt unit [P(7)-Re-Pt(3) = 177.6(1)"in Figure 11. This naturally leads to apparent 3-fold symmetry at the limit of rapid rotation. The activation energy for rotation of the Re(CO)3Lunit of 4 appears to be lower than for 5. Thus, at -80 "C, the 31Presonance due to the dppm phosphorus atoms had split into three broad unresolved resonances, indicating that the fluxionality was not completely frozen out. The difference is most readily interpreted in terms of steric hindrance involving the phosphite ligand leading to slower rotation of the Re(co)3L unit when L = P(OPh13 than with the smaller L = P(OMe)3. The reaction of P(OMe13 with 3 gave a complex mixture of products, which were not identified, while P(OPh)3 failed to react with 3 at room temperature. Reactions with CO. Solutions of the tricarbonyl

Models for Bimetallic Catalysis

Organometallics, Vol. 14, No. 9, 1995 4187

Scheme 1 0

+

0 2

i

+

F

0

+

1

0

12+

C

ti

0

LP'\l/'PC 0

cluster cation 2 in acetone or dichloromethane reacted rapidly with CO to give the tetracarbonyl cluster [Pt3@3-Re(CO)4}01-dppm)31+,6 (eq 1). The reaction was reversible, and bubbling nitrogen through the solution containing 6 led to loss of one carbonyl ligand with formation of 2. This reversibility gives an easy route for enrichment of the cluster with 13C0 and clearly indicates how ligand substitution reactions may occur at the rhenium center of 2. Redissolution of solid samples containing 6 also gave solutions containing mixtures of 2 and 6, so that pure samples of 6 were obtained with some difficulty. These reactions were readily monitored by NMR or IR spectroscopy. Both 2 and 6 are deep red in color, but 6 is slightly darker in color than 2. Complex 6 was stable to excess CO in acetone solution but unstable in dichloromethane, in which further reaction occurred t o give cluster fragmentation and formation of the known cluster [Pt3@3C1)Cu3-CO)01-dppm)31+;8,13 the rhenium-containing product was not identified. Interestingly, as monitored by 31PNMR spectroscopy, the fragmentation appeared t o proceed via an intermediate cluster, which showed a singlet at 6(31P) -23.3. The concentration of this complex grew in the early stages of reaction and then decreased as the final products were formed, so it could not be isolated. It is possible that this complex is formed by addition of a second carbonyl ligand to give [Pts(Re(CO)5}Cu-dppm)31+. The reaction of the PtsMn cluster 3 with CO did not give an identifiable carbonyl adduct. When the reaction was carried out in dichloromethane, the platinum cluster [Pt3@&1)@3-CO)@-dppm)# was formed but no intermediates could be detected.8J0 Again, the formation of this chloro complex is due to the involvement of the solvent used. However, in contrast to the reaction of 2, when complex 3 was treated with CO in acetone, fragmentation of the cluster took place, yielding the known cluster cation [Pt3@3-CO)(CO)01-dppm)3l2+. This (13)ManojloviC-Muir, Lj.;Muir, K. W.; Lloyd, B. R.; Puddephatt,

R.J. J . Chem. SOC.,Chem. Commun. 1985,536.

is known to be formed reversibly by reaction of [Pt3@3C0)01-dppm)3I2+with C0,14 and flushing the acetone with dinitrogen solution of [Pt3013-CO)(CO)01-dppm)3I2+ gave rise to [Pt3013-C0)01-dppm)3I2+.The easier fragmentation of the Pt3Mn cluster is indicative of a weaker Pt-Mn bond in comparison with the corresponding PtRe bond. Both reactions of 2 and 3 can be understood in terms of Scheme 1. Sequential CO additions at rhenium or manganese give the tetracarbonyl and pentacarbonyl clusters, and the next addition occurs at platinum with displacement of [M(C0)51-, M = Mn or Re. The cluster [Pt3(p3-CO)(U-dppm)312+is stable in dichloromethane, so the formation of [Pt3013-C1)013-CO)CU-dppm)31+is probably initiated by reaction of [M(C0)51- with CHzClz with generation of C1-. It should be clear that the reactions shown in Scheme 1are just the reverse of those which are presumably involved in the formation of 2 or 3 from 1 and [M(C0)51-.5 The new complex 6 was characterized spectroscopically. The IR spectrum contained two terminal carbonyl bands [v(CO) = 1995, 1889 cm-'I, shifted to higher frequency compared t o 2 [v(CO) = 1981, 1882, 1871 ~ m - l l ,and ~ no bridging carbonyl bands. The room temperature 31PNMR spectrum of 6 showed a singlet, with complex satellites arising from coupling to lg5Pt that are typical of complexes with metal-metal-bonded Pts(dppm)striangles with apparent C3 The 13C NMR spectrum of 6*, prepared by using 13C0,was more informative. It displayed two carbonyl resonances in a 1:l ratio, a singlet at 6 196 and a more complex resonance at 6 217. The latter resonance appears as an apparent quintet with 1:4:7:4:1 intensities, typical of a group coupled to three equivalent platinum atoms. The observed coupling constant, J(PtC) = 160 Hz, is much too low for a lJ(PtC) coupling but is consistent with a %I(PtReC) c0up1ing.l~ Clearly then, all four carbonyls are bound to rhenium but are in two different (14)Lloyd, B. R.; Bradford, A. M; Puddephatt, R. J. Organometallics 1987,6,424.

4188 Organometallics, Vol. 14, No. 9, 1995 chemical environments, with two showing long-range coupling t o platinum and two not coupled to platinum. These data are mostly consistent with the proposed structure shown in eq 1 with L = CO except, of course, that such a Re(C0)4 unit cannot have C3 symmetry whereas the spectra suggest that this symmetry element is present. The problem is overcome if the cluster is fluxional, undergoing rapid rotation of the Re(C0)4 group with respect t o the P t 3 triangle. To test for this, low-temperature 31P and 13C NMR spectra were recorded. The 31PNMR spectrum of 6 a t -80 "C was far broader than at room temperature, but it did not split into separate resonances. The 13C NMR spectrum did not change significantly a t -80 "C except that the quintet broadened and J(PtC) = 77 Hz was somewhat decreased. These data indicate that rotation of the Re(C0)4 unit was still fairly rapid at -80 "C. The rate of rotation of the Re(C0)sL units in 4-6 appears t o follow the sequence L = P(OPh)3 -= L = P(OMe)3 < L = CO, as expected if the main barrier to rotation is steric hindrance. Reactions with Isocyanides RNC (R = Me, t-Bu, Cy (cyclohexyl), Xy (2,6-MezC&)). The reactions of isocyanide ligands RNC with 2 gave the adducts [Pt3{Re(C0)3(CNR)}@-dppm)31+, 7 (R = Me), 8 (R = t-Bu), 9, (R = Cy), and 10 (R = Xy) by addition to the rhenium center. In contrast, these ligands react with equal molar amounts of the cluster [Pt@&O)@dppm)3I2+ to form the adducts [Pt3(CNR)@&O)@dppm)3I2+by addition a t platinum.12 The reaction of 2 with RNC took about 1/2 h (R = Me, t-Bu, Cy) or 1h (R = Xy) t o reach completion as monitored by NMR spectroscopy. The isocyanide adducts are stable in solution under a Nz atmosphere. The IR spectrum of 10 displayed two terminal carbonyl bands at y(C0) = 1981 and 1874 cm-' and a terminal isocyanide absorption a t 4NC) = 2088 cm-l. Note that the value of v(NC) is lower than in free XyN=C (2115 cm-l), whereas the value of v(NC) in [Pt3013-CO)(XyN~C)@-dppm)31~+ = 2165 cm-l is higher, indicating stronger back-bonding to the isocyanide ligand when coordinated to rhenium. The room temperature 31PNMR spectrum of 10 gave a sharp singlet resonance, but, at -90 "C, this split to give three broad resonances at 6 3.1, -3.0, and -13.1, respectively. The 31PNMR spectrum coalesced at -50 "C. These data are fully consistent with fluxionality as shown in eq 3. The spectroscopic properties of 7-9 are similar, and details are given in the Experimental Section. In all cases the values of 4NC) were lower than in the free ligands (2144, 2102, and 2120 cm-l for 7-9, respectively, compared to 2167, 2140, and 2145 cm-l for free MeNC, t-BuNC, and CyNC in CHzClz solution, respectively), indicative of coordination to the rhenium center in all cases. Reactions with Thiols RSH (R = Et, t-Bu or 3-MeCdI.d. The thiol ligands RSH reacted with cluster 2 to give the adduds 11-13, R = Et, t-Bu, or 3-MeC&, respectively (eq 1). The reaction rates followed the sequence R = Et (secondsto complete) > t-Bu (minutes) > 4-MeCsHs (1h), as monitored by 31PNMR spectroscopy. In contrast, the thiol ligands RSH (R = Et and Ph) react with [Pt(~~-CO)(~-dppm)31~+ to form Pt3(SHR)@3-CO)@-dppm)3I2+, which then readily transforms to the stable [Pt3H@3-SR)@3-CO)(-dppm)312+.8J2

(15)(a) Caulton, K.G. Coord. Chem. Rev. 1981,38,1. (b) Bruce, M. I. Chem. Rev. 1991,91, 197.

Organometallics, Vol. 14,No. 9,1995 4189

Models for Bimetallic Catalysis

A the plane of symmetry remains even with an unsymmetrical alkyne and so this should give only three 31P resonances. The observation of six resonances is therefore strong evidence for structure B. It is noted that alkynes react with complex 1 a t the Pt3 triangle and so give rise to very different products containing triply bridging alkyne ligands.8J6 The reactions of HCCH and PhCCH with 3 gave an unidentified mixture of products. Ligand Exchange Reactions. The cluster 6 can undergo ligand for carbonyl exchange according to Scheme 2 (L = CO) on reaction with ligands L' (L' = P(OMe)3, P(OPh)3, HCCH, HCCPh) by substitution a t rhenium while reactions with halide (X = C1, Br, I) lead to displacement of L = CO from rhenium with addition of X- a t platinum. These substitution reactions are all substantially slower than the analogous addition reactions to cluster 2. Similarly, the cluster [Pt3{Re(C0)3(HCCH)}(U-dppm)31+,14, reacted slowly (ca. 14 and 24 h to completion when R = Me or Ph respectively) with P(OR)3(R = Me and Ph) by displacement of acetylene to give 4 or 5 respectively. The rates followed the sequence 2 >> 6 >> 14 in reactions with the phosphite ligands. The reactions with 14 are presumed to be associative since 14 is stable to dissociation of acetylene. Carbon monoxide did not displace acetylene from 14.

Scheme 2 O

O

1+

c_c

a

L = P(OR)3 or HCCH; X = C1, Br, or I.

two donor-acceptor bonds are possible as shown in D.17 Hence, weaker Pt-Re bonding is expected in 6 than in

Discussion L

The cations 2 and 3 are coordinatively unsaturated 54-electron ~ l u s t e r s . ~The bonding in 2 has been interpreted in terms of the three filled M-M bonding orbitals of the Pt&-dppm)s fragment (a1 e symmetry) acting as donors to the three vacant acceptor orbitals of the Re(C0)3+ fragment (also a1 e symmetry) as shown in C.5 In this way, each Pt atom shares 16 and

+

D

(i) al'

+

(ii) e' + b l

a1

L

+

LX

L L

(iii) e'

2, consistent with the observed increase in Pt-Re bond distances in 5 compared to 2. This interpretation also C

the Re atom shares 18 valence electron^.^ It might be expected that ligands would therefore add selectively to platinum in much the same way as has been observed in trinuclear complexes such as [Pt3Cu3-CO)Cu-dppm)312+.8 However, all the ligands studied in this work add selectively a t rhenium (eq 1). It is interesting to ask why. Consider first the bonding in the products, all of which probably have a 56-electron count (the possibility of the alkyne acting as a 4-electron donor has not been disproved). Complex 6 is the simplest example. The bonding may still be considered in terms of the Pt3(Udppm)3 fragment acting as a donor to the Re(C0)4+ fragment, but this has only two acceptor orbitals so only (16)ManojlovibMuir, Lj.; Muir, K. W.; Rashidi, M.; Schoettel, G.; Puddephatt, R. J. Organometallics 1991,10,1719.

rationalizes the slippage of the rhenium from the center of the Pt3 triangle in 5. Another way of looking a t this is to consider that the LUMO in 2 is a cluster antibonding orbital of e symmetry and considerableRe character. Donation of two electrons into such an orbital will naturally weaken the cluster b ~ n d i n g .It ~ should be pointed out that if the ligand did add below the P t 3 plane it could donate electron density into one or more of the empty p-orbitals on platinum and this need not weaken the cluster bonding; this is what happens when ligands add to the Pt3 cluster 1.8 There is another useful analogy to this chemistry. The proposed donor orbitals of the Pt&-dppm)3 fragment have a1 e symmetry and so do the donor orbitals of C5H5- or c ~ H 6 . lHence, ~ in the limit, it could be argued that the cluster 2 is isolobal to [CpRe(CO)31.This

+

(17)For previous theoretical work on PtsLs clusters and on M(CO), fragments, see: (a)Evans, D. G. J. Organomet. Chem. 1988,352,397. (b) Mealli, C. J. Am. Chem. SOC.1985,107,2245. (c) Albright, T. A.; Burdett, J. K.; Whangbo, M.-H. Orbital Interactions in Chemistry; Wiley: New York, 1985;Chapter 20.

Xiao et al.

4190 Organometallics, Vol. 14, No. 9, 1995 complex is inert to ligand addition but the related complex [CpRe(CO)(NO)Rlis known t o add ligands a t rhenium with slippage of the v5-C5H5 ligand to q3 and then q1.ls The ligand addition to 2 could be considered analogous to this chemistry. Hence, the addition of one or two ligands t o 2 might lead to slippage of the Re(C0)3L, unit from v3 (n = 0)to v2 (n= 1)and q1 (n = 2) with respect to the P t 3 triangle. The R3Mn complex 3 appears to have weaker metal-metal bonding, and ligand addition appears to occur with cleavage of the manganese fragment from the cluster. In an additional analogy, rotation of v5-C5H5ligands about the Cp-metal axis is known to occur with a very low activation energy so it might be predicted that the Pts&-dppm)3'ligand" should rotate easily about the RePt3 centroid axis in 2. There is no easy way to study this reaction which, of course, is equivalent to rotation of the Re(C0)3unit about the P t 3 triangle. A somewhat higher activation energy might be expected for rotation of the Re(C0)3Lunits in 4-8, since the analogy here is to q3-Cpligands. Nevertheless, the complexes 4-6 are all fluxional and only the alkyne complexes 7 and 8 are not. A related fluxionality has been observed previously for the clusters [Pt401-H)01-C0)201-dppm)3Ll+,in which the Pt(C0)zL group migrates from edge to edge of the dppm-bridged P t 3 triangle.lg The above arguments, based on analogies only, are supported by EHMO calculations on the model cluster [Pt3(CO)&-Re(CO)4}lf,substituting two carbonyl ligands for each p-dppm ligand in 6 and with initial geometry E. An energy correlation diagram is shown as Figure 0 0

c c

\;

E

OC

0

c c

0

\I/

F

4. The 2a1 acceptor orbital of the [Re(COW+fragment17 overlaps with the lal' donor orbital of the [Pt3(co)61 fragment17to give the bonding orbital 3a', which is the HOMO. The lbl acceptor orbital of the [Re(CO>41+ fragment overlaps with one of the le' donor orbitals of the [Pt3(CO)6]fragment t o give the bonding orbital 2a'. Both of these effects contribute to Pt-Re bonding, and it is the lbl-le' overlap which leads to asymmetry in the Pt-Re bonding. The other e' donor orbital is destabilized by a four-electron interaction with one of the filled "t&ike" orbitals of the d6 [Re(CO)4]+fragment (note that the net repulsive interaction is also reduced by slippage of the Re(co)4group). Rotation of the [Re(C0)41+fragment is calculated to have a low activation barrier, since, as overlap of l b l with one of the le' donors decreases, overlap with the other increases, and the energies of the frontier orbitals change only slightly (18)(a) Casey, C. P.; OConnor, J. M.; Jones, W. D.; Haller, K. J. Organometallics 1985, 2, 535. (b) Bang, H.; Lynch, T. J.; Basolo, F. Organometallics 1992, 1 1 , 40. (c) Biagioni, R. N.; Lorkovic, I. M.; Skelton, J.; Hartung, J. B. Organometallics 1990,9,547. (d) O'Connor, J. M.; Casey, C. P. Chem. Rev. 1987,87,307. (19) Douglas, G.; ManojloviC-Muir, Lj.; Muir, K. W.; Jennings, M. C.; Lloyd, B. R.; Rashidi, M.; Schoettel, G.; Puddephatt, R. J. Organometallics 1991, 10, 3927.

IPt3(COkl

lPt3(COk{Re(COh)lt

IRe(COh]+

Figure 4. Energy correlation diagram for interaction of D3h [Pt3(Co)S] and czu[Re(C0)4]+fragments to give c, [Pt3(CO)6{Re(C0)4}]+. For frontier orbitals, see D. during the rotation between limiting structures E and

F. Note, however, that the rhenium is expected to move during the rotation to remain away from the center of the P t 3 triangle. The preferred orientation may be determined by steric effects, by the semibridging carbonyl effects or by changes in energy due to slippage of the Re atom with respect t o the Pt3 triangle. The EHMO method is not well suited to geometry optimization so these effects have not been pursued, though it should be clear from the le'-bl overlap shown in D why the slippage of rhenium toward an edge of the Pt3 triangle is favored. The observation that Pt3Re cluster 2 is reactive at the rhenium center was unexpected. It is not known what role each metal plays in the heterogeneous Pt/Re catalysts, but, on the basis of the model complex 2, an active role for the rhenium atoms may be envisaged.20

Experimental Section The compounds [Pt3{M(C0)3}@-dppm)31+(M= Re, 2; Mn,

3)were prepared by the previously reported p r ~ c e d u r e .IR ~ spectra were recorded by using a Perkin-Elmer 2000 spec-

trometer, and the NMR spectra were recorded in CDzClz solution a t ambient temperature, unless otherwise indicated, with a Varian Gemini-300 spectrometer; chemical shifts are referenced to TMS ('H) and 85%HaPo4 (31P{1H}). Elemental analyses were performed by Galbraith Laboratories, Inc. [ P ~ ~ { R ~ ( C O ) S ( P ( O M ~ ) ~ ) } ~ - ~ ~ ~To~a) ~ I [ P F ~ I solution of 2 (30 mg) in CHzClz (10 mL) was syringed P(OMe13 (0.1 mL). The solution immediately darkened slightly. The mixture was stirred for 15 min, the solution was concentrated, and the product was precipitated as a deep brown solid by addition of pentane and then washed with pentane and dried under vacuum. It was recrystallized from CHzClfiexane. Yield: 70%. Anal. Calcd for C83H7906FsP7C12RePt3: C, 40.7; H, 3.2. Found: C, 40.8; H, 3.4. IR (Nujol): v(CO)/cm-' = 1943 s, 1877 m, 1856 vs. NMR in CDzC12: d(lH) 6.40 [m, HzCPZI; 4.72 [m, HzCPz]; 3.10 [d, 3J(PH) = 17 Hz,P(OCH3)31; W P ) 130.5 [quin, %J(PtP) = 157 Hz, P(OMe)31; -5.6 [s, 'J(PtP) = (20) Bond, G. C. Chem. SOC.Rev. 1991,20, 441.

Organometallics, Vol. 14, No. 9, 1995 4191

Models for Bimetallic Catalysis

Table 2. Crs'stalloaaDhic Data for

3028 Hz, 3J(PP)= 186 Hz, dppml; 6 P P , -80 "C) 132.2 [m, 2J(PtP)= 156 Hzl; 1.1,-2.4, -15.6 [br, dppml. [Pt~{Re(C0)~(P(OPh)~)}(p-dppm)~l[PF~l. Complex 5[PFel was prepared in a similar way except that the reagent P(OPh)3 was used. It was recrystallized from CHnClddiethyl ether. Yield: 85%. Anal. Calcd for C96H8106F6P7RePt3: c, 48.8; H, 3.3. Found: C, 48.5; H, 3.7. IR (Nujol): v(CO)/cm-I = 1955 m, 1899 m, 1868 s. NMR in CD2C12: 6PH) 6.45 [m, H2CP21; 4.75 [m, H2CP21; 6(31P)111.8 [quin, 2J(PtP)= 194 Hz, P(OPh)31; -5.5 [s, 'J(PtP) = 3007 Hz, 3J(PP)= 195 Hz, dppml; W P , -80 "C) 114.1 [tquin, WPtP) = 300 Hz, 135 Hz, P ( 0 P h ) ~ l1.3 ; [s, br, 'J(PtP) = 3577 Hz, dppml, -3.7 [m, 'J(PtP) = 2833 Hz, dppml, -16.7 [m, WRP) = 2688 Hz, dppml. [Pt3{Re(CO)4}@-dppm)3][PFsl.CO was bubbled through a solution of 2 (15 mg, 0.007 mmol) in CDzCl2 (0.5 mL) in an NMR tube for 1 min. The solution became slightly darker in color. NMR spectra ('H and 31P{1H})indicated the immediate disappearance of 1 and the quantitative formation of 6. This reaction was reversible, as evidenced by the fact that, in the absence of CO, complex 2 was slowly regenerated at the expense of 6 in the solution. IR (CH2C12): v(CO)/cm-'= 1995 s, 1889 vs. NMR: W H ) 6.35 [m, H2CP21; 4.60 [m, H2CP21; 6 P P ) -2.6 [s, 'J(PtP) = 3000 Hz, 3J(PP)= 194 Hz, dppml; 6 ( W ) 216.5 [quin, V(PtC) = 81 Hz, C'O], 195.6 [s, C201; 6(31P, -80 "C) -2.8 [br, 'J(PtP) = 3120 Hz, dppml; W3C, -80 "C) 217.3 [m, 2J(PtC)= 77 Hz, C'OI, 196.8 [s, C201. Addition of CO to the CD2C12 solution of 6 for a longer period led to the complete conversion to the previously characterized complex, [Pt3(~(3-Cl)CU~-CO)(~(-dppm)31+, within 1 5 min.I4 The reaction of complex 3 with CO was carried out similarly. When the reaction was conducted in CDzCl2 in an NMR tube, the formation of [Pt3(p3-C1)(~3-C0)~-dppm)3lt was occurred rapidly and in almost quantitative yield, a s monitored by NMR. When this reaction was carried out using a n acetone solution, the product was [Pt3(p3-CO)(CO)(~-dppm)3I2+ which, upon flushing with dinitrogen, was converted to [Pt3(p&O)(pu-dppm)3l2+.Both compounds are known and they were identified by their 'H and 31PNMR spectra.14 [Pt3{Re(CO)3(MeNC)}@-dppm)sl[PFs].To a solution of 2 (36 mg, 0.017 mmol) in acetone (15 mL) was added MeNC (0.8 pL, 0.017 mmol) via microsyringe. The color of the red solution darkened immediately. After 0.5 h of being stirred, the solution was concentrated to ca. 1 mL under vacuum. Hexane was added to precipitate the product, which was further washed with diethyl ether followed by vacuum drying to give the product a s a n orange-yellow powder in 87% yield. Anal. Calcd for C ~ O H ~ ~ F ~ N O & c, P ~43.78; ~ R ~ :H, 3.17. Found: C, 43.65; H, 3.16. IR (Nujol): v(C0)lcm-' = 1981 s, 1879 vs, br; v(NC)lcm-' = 2144 s. NMR in (CD&CO: 6('H) 6.64 [br, 3H, HaCP2], 4.58 [br, 3H, HbCP21,2.60 [s, 3H, CH31; 6(31P{'H}) -2.5 [s, 6P, 'J(PtP) = 2940, 2J(PtP)= 255, 3J(PP) = 189 Hz, dppml. [Pt3{Re(CO)s(t-BuNC)}@-dppm)sl [PFs]. The same procedure a s above was followed with the use of t-BuNC instead of MeNC. The product was obtained was orange-yellow powder. Yield: 80%. Anal. Calcd for C83H75F~N03P7Pt3Re: C, 44.57; H, 3.38. Found: C, 44.30; H, 3.25. IR (Nujol): v(CO)/ cm-' = 1983 s, 1869 VS, br; v(NC)/cm-' = 2102 s. NMR in (CD3)2CO: 'H, 6 = 6.63 [br, 3H, H"CP21, 4.61 [br, 3H, HbCP21, 0.91 [s, 9H, C(CH&]; 6(31P{'H}) -2.1 [s, 6P, 'J(PtP) = 2975, 2J(PtP)= 235, 3J(PP)= 206 Hz, dppml. [Pts{Re(CO)s(CyNC)}~-dppm)~l[PFsl. This was prepared similarly and isolated as a n orange-yellow powder. Yield: 76%. Anal. Calcd for C85H77F~N03P7Pt3Re:c , 45.12; H, 3.43. Found: C, 44.9; H, 3.2. IR (Nujol): v(C0)lcm-' = 1980 s, 1876 s, sh, 1869 s; v(NC)lcm-' = 2192 s. NMR in (CD3)2CO: W H ) 6.30 [br, 3H, HaCP21, 4.63 [br, 3H, HbCP21, 1.600.80 [m, 11H, C ~ I ~6(31P{1H}) ] ; -2.3 [s, 6P, 'J(PtP) = 2981, 2J(PtP)= 255, 3J(PP)= 187 Hz, dppml. [Pt3{ Re(CO)s(2,6-Me&&I~NC)}(p-dppm)sl[PF~. This was prepared in a similar way except that 2,6-xylyl isocyanide was used. Yield: 82%. Anal. Calcd for Cs7H75F6N03P7Pt3Re: C,

empirical formula fw space group

C98H87FsO~P8Pt3Re 25_10.0

a,A

13.993(1) i7.a68( 1) 19.753(2) 88.198(7) 87.766(7) 72.394(4) 4702.9(7) 2 2428 1.772 0.33 x 0.25 x 0.15 23 Mo Ka 0.719 73 59.93 0.75 to 1.20 2.4 to 30.5 14765 464 0.0405 0.0429 1.53 0.10 -0.94 to 1.19

b, A

c,

A

a,deg A deg Y,deg

v, A3

z

F(000) g cm-3 cryst dimens, mm3 temp, "C radiation wavelength, A p(Mo Ka),cm-I abs corr factors on F data collcn range, 0 (deg) no. of reflns in refinement [I > 3dZ)I no. of params refined Dealed,

R RW

observation of unit wt largest shiftlesd ratio final difference synthesis, e A-3

P1

45.73; H, 3.31. Found: C, 45.68; H, 3.46. IR (Nujol): v(C0)l cm-l = 1981 s, 1874 vs, br; v(NC)lcm-l = 2088 s. NMR in (CD&CO: 6('H) 6.30 [m, 3H, H"CP21, 4.73 [m, 3H, HbCP21, 2.60 [s, 6H, (CH&C6H3NC]; C~(~'P{'H)), -2.5 [s, 6P, 'J(PtP) = 3026, 2J(PtP)= 227, 3J(PP)= 182, dppml; W H , -90 "C) 6.09 [br, 2H, HaCP2], 5.31 [br, l H , H"'CP21, 4.84 [m, 2H, HbCP21, 4.55 [br, l H , Hb'CP21; 6(31P{1H}, -90 "C) 3.1 [br, 2P, dppml, -3.0 [br, 2P, dppm], 13.1 [br, 2P, dppml; 31P{1H} NMR spectrum coalesced a t -50 "C, 6 = -2.9 [br, 6P, 'J(PtP) = 2992 Hz, dppml. [Pts{Re(C0)3(3-MeC&SH)}(p-dppm)~l[PF~l. To a solution of 1 (34 mg, 0.016 mmol) in acetone (15 mL) was added 3-toluenethiol(1.9 pL, 0.016 mmol) via microsyringe. The color of the red solution became more intense immediately. After 0.5 h of being stirred, the solution was concentrated to ca. 1 mL under vacuum. Hexane was added to precipitate the product, which was further washed with diethyl ether followed by vacuum drying to give the product a s an orange-red powder in 85% yield. Anal. Calcd for C85H74F603P7Pt3ReS: C, 44.82; H, 3.27. Found: C, 45.11; H, 3.10. IR (Nujol): v(C0)lcm-I = 1997 s, 1897 s, sh, 1883 s; NMR in ( C D ~ Z C OW : H ) 6.28 [m, 3H, 2J(PH)= 54, HaCP2], 4.67 [m, 3H, HbCP21;6(31P{1H})-1.9 [s, 6P, WPtP) = 3028, 2J(PtP)= 213, 3J(PP)= 171, dppml; W H , -90 "C 6.22 [br, 3H, H"CP21, 4.55 [br, 3H, HbCP21; 6(31P{1H},-90 "C) -2.2 [br, 6P, 'J(PtP) = 3080 Hz, dppml. [Pt3{Re(CO)3(C2H5SH)}@-dppm)31[PFsl. This was prepared similarly. Anal. Calcd for C B O H ~ ~ F ~ O ~ P C, ~P~~R~S: 43.36; H, 3.28. Found: C, 43.16; H, 3.12. IR (Nujol): v(C0)l cm-l = 1979 s, 1869 s, br; NMR in (CD3)zCO: 6(lH), 5.81 [m, 3H, HaCP2], 5.44 [m, 3H, HbCP2], 1.86 [quar, 2H, 3J(HH) = 7.3, CH2 of C2Hb1, 1.11 [t, 3H, 3J(HH) = 7.3, CH3 of CzHsl; C~(~'P{'H}) -1.9 [s, 6P, 'J(PtP) = 2948, 'J(PtP) = 187, 3J(PP) = 199, dppml. [Pts{Re(CO)s(t-BuSH)}(p-dppm)~l[PFsl. This was prepared similarly. Anal. Calcd for C ~ O H ~ ~ F ~ O & P c, ~~R~S: 43.89; H, 3.41. Found: C, 44.17; H, 3.58. IR (Nujol): v(C0)l cm-I = 1983 s, 1876 s, br; NMR in (CD&CO: 6PH) 6.32 [br, 3H, HaCP2], 4.69 [m, 3H, HbCP21, 1.39 [s, 9H, CH31; c ~ ( ~ ' P { ~ H } ) -1.9 [s, 6P, 'J(PtP) = 3026, 2J(PtP)= 198, 3J(PP)= 176 Hz, dppml. [Pt3{Re(CO)3(HC~CH)}@-dppm)3][PFsl. Acetylene was bubbled through a solution of 2 (30 mg) in CHzClz (10 mL) for 1min, immediately causing a color change to dark brown. The mixture was stirred for 15 min, the volume was reduced to

4192 Organometallics, Vol. 14, No. 9, 1995

Xiao et al.

Table 3. Atomic Fractional Coordinates and Displacement Parameters (k) for Atoms in the Phenyl Groups and Solvent Molecule [C(A)-C(OB), C(lS), C(2S1, and O(S)l atom X Y z U atom X Y 2 U 0.09857(2) 0.16111(2) 0.11056(2) 0.29575(2) 0.16276(16) 0.10266(14) 0.13759(15) 0.10885(15) -0.02023(15) 0.03969(15) 0.43879(15) 0.4465(2) 0.3567(7) 0.3749(9) 0.4800(7) 0.4089(8) 0.5068(10) 0.5314(9) 0.4342(4) 0.4785(4) 0.5462(4) 0.4107(5) 0.3555(4) 0.2423(5) 0.8429(14) 0.786(2) 0.7022(14) 0.1840(6) 0.1537(6) 0.0179(6) 0.3687(7) 0.3273(6) 0.2546(6) -0.0818(6) -0.1334(4) -0.2280(6) -0.2711(6) -0.2195(4) -0.1248(7) 0.1234(4) 0.1088(7) 0.1809(7) 0.2676(4) 0.2822(7) 0.2101(8) -0.0110(4) -0.1030(5) -0.1900(5) -0.1850(4) -0.0930(5) -0.0060(5) 0.1604(8) 0.1007(6) 0.1440(6) 0.2469(7) 0.3067(5) 0.2634(7) 0.0442(6) -0.0397(4) -0.1329(6) -0.1422(6) -0.0583(5)

0.22934(2) 0.22307(2) 0.35599(2) 0.23129(2) 0.09659(12) 0.10006(11) 0.42667(11) 0.28435(13) 0.30118(12) 0.43991(12) 0.13469(12) 0.3500(2) 0.3761(6) 0.3201(7) 0.2682(5) 0.4290(6) 0.3835(9) 0.3269(7) 0.0488(3) 0.1174(3) 0.1339(3) 0.3448(4) 0.2470(4) 0.2316(5) 0.2216(11) 0.221(1) 0.2167(11) 0.0432(4) 0.3709(5) 0.3874(5) 0.3009(6) 0.2394(5) 0.2298(5) 0.5131(5) 0.5129(6) 0.5650(4) 0.6174(4) 0.6176(5) 0.5655(3) 0.4936(5) 0.5713(3) 0.6068(4) 0.5645(4) 0.4868(3) 0.4513(4) 0.0692(5) 0.1244(3) 0.1045(5) 0.0293(4) -0.0260(3) -0.0060(5) 0.0488(4) 0.0428(5) 0.0067(6) -0.0234(4) -0.0173(5) 0.0188(7) 0.0903(5) 0.1500(4) 0.1519(6) 0.0941(5) 0.0344(5)

0.17596(1) 0.30296(1) 0.23544(1) 0.19908(2) 0.32031(10) 0.17 144(10) 0.32465(10) 0.40379(11) 0.10641(1) 0.14921(10) 0.17581(10) 0.5820(2) 0.5342(5) 0.6307(5) 0.5491(6) 0.6187(6) 0.5346(7) 0.6283(8) 0.1972(3) 0.0979(3) 0.2048(3) 0.1554(4) 0.3484(3) 0.0479(3) 0.6671(10) 0.730(1) 0.7784(9) 0.2396(4) 0.4072(4) 0.0751(4) 0.1722(5) 0.2959(4) 0.1050(4) 0.1614(6) 0.2223(5) 0.2322(3) 0.1811(5) 0.1201(4) 0.1103(4) 0.1115(3) 0.1262(6) 0.1070(4) 0.0731(3) 0.0584(5) 0.0776(4) 0.1845(4) 0.1753(3) 0.1878(5) 0.2096(3) 0.2188(4) 0.2063(6) 0.0943(4) 0.0421(6) -0.0171(4) -0.0240(4) 0.0282(5) 0.0874(3) 0.3566(6) 0.3380(3) 0.3648(6) 0.4103(5) 0.4289(4)

0.031 0.031 0.031 0.037 0.037 0.035 0.039 0.038 0.037 0.040 0.042 0.073 0.163 0.192 0.178 0.181 0.253 0.257 0.051 0.050 0.048 0.075 0.069 0.080 0.256(8) 0.21(1) 0.152(6) 0.041 0.043 0.045 0.056 0.052 0.051 0.046(2) 0.051(2) 0.069(3) 0.077(3) 0.074(3) 0.065(3) 0.049(2) 0.065(3) 0.084(3) 0.082(3) 0.076(3) 0.063(3) 0.042(2) 0.055(2) 0.070(3) 0.069(3) 0.077(3) 0.064(3) 0.040(2) 0.055(2) 0.067(3) 0.064(3) 0.087(3) 0.071(3) 0.049(2) 0.062(3) 0.095(4) 0.108(4) 0.114(5)

C(E6) C(F1) C(F2) C(F3) C(F4) C(F5) C(F6) C(G1) C(G2) C(G3) C(G4) C(G5) C(G6) C(H1) C(H2) C(H3) C(H4) C(H5) C(H6) C(I1) C(I2) C(I3) C(I4) C(I5) C(I6) C(J1) C(J2) C(J3) C(J4) C(J5) C(J6) C(K1) C(K2) C(K3) C(K4) C(K5) C(K6) C(L1) C(L2) C(L3) C(L4) C(L5) C(L6) C(M1) C(M2) C(M3) C(M4) C(M5) C(M6) C(N1) C(N2) C(N3) C(N4) C(N5) C(N6) C(O1) C(02) C(03) C(04) C(05) C(06)

0.0350(7) 0.2617(4) 0.3285(6) 0.4077(6) 0.4200(4) 0.3532(6) 0.2740(6) 0.5118(7) 0.5040(8) 0.5779(5) 0.6597(6) 0.6676(7) 0.5937(4) 0.4980(4) 0.4569(7) 0.4746(8) 0.5333(4) 0.5744(7) 0.5568(8) 0.5587(9) 0.5710(8) 0.5863(4) 0.5894(7) 0.5771(7) 0.5618(5) 0.1605(5) 0.2510(4) 0.2921(5) 0.2428(5) 0.1523(4) 0.1111(6) 0.0431(7) -0.0386(4) -0.1159(5) -0.1116(6) -0.0299(3) 0.0474(6) -0.0248(6) -0.0587(5) -0.1580(7) -0.2234(6) -0.1894(6) -0.0902(8) 0.2536(4) 0.3021(5) 0.3848(6) 0.4191(4) 0.3706(5) 0.2878(7) -0.1482(6) -0.2180(6) -0.3161(4) -0.3445(5) -0.2747(5) -0.1766(5) -0.0414(9) -0.1236(7) -0.1340(5) -0.0622(7) 0.0200(6) 0.0304(6)

0.0325(7) 0.0273(6) 0.0566(3) 0.0062(5) -0.0734(5) -0.1027(3) -0.0523(6) -0.0230(5) -0.0738(3) -0.1446(4) -0.1646(5) -0.1137(3) -0.0429(5) 0.1704(4) 0.1750(6) 0.2265(7) 0.2734(4) 0.2688(7) 0.2173(8) 0.1564(7) 0.1028(5) 0.1244(4) 0.1995(6) 0.2531(4) 0.2315(6) 0.2278(6) 0.2291(3) 0.1811(6) 0.1317(5) 0.1304(4) 0.1784(7) 0.5211(4) 0.5251(3) 0.5944(3) 0.6598(3) 0.6558(3) 0.5865(3) 0.3267(5) 0.3443(7) 0.3854(5) 0.4089(4) 0.3914(6) 0.3503(4) 0.4554(5) 0.4653(3) 0.4921(6) 0.5089(4) 0.4990(4) 0.4722(7) 0.3447(4) 0.3973(4) 0.4267(6) 0.4035(4) 0.3509(4) 0.3215(6) 0.2569(6) 0.2303(3) 0.1918(5) 0.1798(5) 0.2064(3) 0.2449(6)

0.4021(7) 0.3687(5) 0.4005(4) 0.4344(3) 0.4366(4) 0.4048(3) 0.3709(3) 0.2006(7) 0.2531(6) 0.2611(3) 0.2166(6) 0.1641(5) 0.1561(4) 0.0518(4) -0.0112(3) -0.0601(4) -0.0461(3) 0.0169(3) 0.0658(4) 0.2697(2) 0.3230(4) 0.3872(4) 0.3981(2) 0.3448(4) 0.2806(4) 0.4794(5) 0.5039(2) 0.5580(4) 0.5878(4) 0.5633(3) 0.5092(5) 0.3436(3) 0.3864(4) 0.3915(4) 0.3539(5) 0.3112(3) 0.3060(5) 0.4235(6) 0.4894(5) 0.5027(3) 0.4501(5) 0.3843(4) 0.3710(4) 0.3185(4) 0.3755(3) 0.3691(3) 0.3057(3) 0.2487(2) 0.2551(3) 0.1399(6) 0.1004(3) 0.1238(5) 0.1868(5) 0.2263(3) 0.2029(6) 0.0270(3) 0.0213(4) -0.0361(3) -0.0879(3) -0.0822(4) -0.0248(3)

0.095(4) 0.044(2) 0.050(2) 0.066(3) 0.060(2) 0.072(3) 0.060(2) 0.051(2) 0.078(3) 0.094(4) 0.086(3) 0.096(4) 0.074(3) 0.053(2) 0.074(3) 0.112(4) 0.116(5) 0.102(4) 0.072(3) 0.050(2) 0.069(3) 0.088(3) 0.084(3) 0.076(3) 0.064(3) 0.045(2) 0.055(2) 0.064(3) 0.085(3) 0.097(4) 0.072(3) 0.044(2) 0.052(2) 0.065(3) 0.066(3) 0.075(3) 0.060(2) 0.043(2) 0.063(3) 0.081(3) 0.084(3) 0.078(3) 0.057(2) 0.044(2) 0.060(2) 0.071(3) 0.073(3) 0.067(3) 0.053(2) 0.041(2) 0.062(2) 0.080(3) 0.085(3) 0.080(3) 0.051(2) 0.045(2) 0.057(2) 0.074(3) 0.077(3) 0.074(3) 0.058(2)

a U is the isotropic displacement parameter, and for other atoms U = I13 ~.13=l~j3=,U,u:u,*(~,.;i,,. Atoms in the solvent molecule are labeled by S .

about 2 mL, followed by precipitation of the product as a dark brown solid using pentane. It was washed with pentane, dried under vacuum, and recrystallized from CHzClddiethyl ether. Yield: 90%. Anal. Calcd for CsoH&3F6P7RePt3: C, 44.1; H, 3.2. Found: C, 43.9; H, 2.8. IR (Nujol): v(CO)/cm-' = 1979 s, 1886 s, 1867 s. NMR in CD2Clz: W H ) 6.00 [br, 2H, HzCZI; 5.87 [br, H2CP21; 4.95 [br, H2CP21; 3.92 [m, HzCPZI;6(31P)25.2 [m, WPtP) = 3073 Hz, dppm], -1.1 [m, 'J(PtP) = 2462 Hz, dppm], -15.3 [m, lJ(PtP) = 4567 Hz, dppml; W3C) 85.2 (br, HzCz).

[P~~(R~(CO)~(P~C~CH)}~-~~~~ This )~~[PF~I. was prepared in a similar way except t h a t the reagent phenylacetylene (0.2 mL) was used. The complex was recrystallized from CHzClddiethyl ether. Yield: 70%. Anal. Calcd for Cs7H&3F6P&1~RePt3: C, 44.6; H, 3.1. Found: c , 44.9; H, 3.2%. IR (Nujol): v(CO)/cm-I = 1977 vs, 1882 s, 1863 s. NMR in CDzClz: d('H) 5.50 [br, l H , PhCfl; 5.18 [m, 2H, HzCP21; 4.31 [m, 2H, HzCPz]; 3.88 [m, 2H, HzCP21; 6(31P)21.3 [m, 'J(PtP) = 3037 Hz, dppml, 13.9 [m, 'J(PtP) = 3100 Hz, dppml, -0.4 [m, lJ(PtP) = 2575 Hz, dppml; -6.3 [m, 'J(PtP)

Models for Bimetallic Catalysis

Organometallics, Vol. 14,No. 9, 1995 4193

= 2502 Hz, dppm], -16.9 [m, 'J(PtP) = 4494 Hz, dppm], -20.5 [m, 'J(PtP) = 4494 Hz, dppm]. Reactions of [Pt~{Re(CO)~}(2c-dppm)~l[PF~l. To a solution of 6 (28 mg, 0.013 mmol) in acetone (0.5 mL) was added EtrNBr (2.7 mg, 0.013 mmol). A brown precipitate formed immediately with the evolution of CO. This precipitate was further washed with acetone (0.5 mL) to give [Pts(ps-Br){Re(CO)s}(U-dppm)3]as a red brown powder, identified by its NMR and IR spectra. Yield: 70%. Similar reactions of 6 with EtdNCl and Bu4NI give complexes [Pt3(~3-Cl)(Re(CO)3}(pdppm)sl in 55%yield and [Pt3(U3-I){Re(C0)3}(U-dppm)31 in 80% yield, respectively. Similarly, reaction of 6 (35 mg, 0.016 mmol) in acetone (15 mL) with P(OMe)3 (1.9 pL, 0.016 mmol) gave [Pts{Re(CO)s(P(OMe)3)}(p-dppm)31[PF6] in 88% yield. The product was characterized by its NIvIR and IR spectra. Similar reactions with P(OPh)3, HCCH and PhCCH afforded [Pts{Re(CO)a(P(OPh)3)}(U-dppm)31[PF6] in 85%yield, [Pt3{Re(C0)3(HCCH)}(U-dppm)s][PF6] in 90% yield and [Pt3{Re(C0)3(PhCCH)}(CLdppm)3][PFs] in 87% yield, respectively. Reactions of [Pt3(Re(CO)3(HCCH)}(pc-dppm)3][PF6l with P(OMe)3or P(OPh)3to give [Pt3CRe(C0)3(P(OMe)3)}(U-dppm)al[PFsl or [PtdRe(CO)s(P(OPh)3)}Ol-dppm)3l[PF~] were carried out in a similar way. X-ray Crystal Structure Analysis of 5[PF&EtOH. The crystal was a red chunk of approximate dimensions 0.33 x 0.25 x 0.15 mm3. The X-ray crystallographic measurements were made a t 23 "C, with graphite-monochromated Mo K, radiation and a n Enraf-Nonius CAD4 diffractometer. The unit cell constants (Table 2) were determined by a leastsquares treatment of 25 reflections with Bragg angles 20.8 < e < 22.9". The intensities of diffracted beams were measured by continuous 9/26 scans of width (0.99 0.59 tan 8)' in 8. The scan speeds were adjusted to give dZ)/Z< 0.03, subject to a time limit of 30 s. Intensities of three reflections, remeasured every 2 h, decreased by 21% of their mean initial value during the data collection. The intensities of all reflections, derived in the usual manner (q = 0.03),21were corrected for Lorentz, polarization, and crystal decomposition effects. The absorption correction was made at the end of isotropic refinement, using the empirical correction of Walker and Stuart.22 The 6187 symmetry-related reflections were averaged to obtain 2999 independent ones and R(merge) = 0.031.

+

(21) ManojloviC-Muir, Lj.; Muir, K. W. J . Chem. SOC.,Dalton Trans. 1974, 2427. (22) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.

Of 28 429 unique reflections measured, only 14 765 with Z > in the structure analysis. The positions of the platinum and rhenium atoms were determined from a Patterson function and those of the remaining non-hydrogen atoms from the subsequent difference Fourier syntheses. Hydrogen atoms were included in the structural model in calculated positions, and their displacement parameters were fixed at U(H) = 1.2 U(C), where U(C) is the equivalent isotropic displacement parameter of the carbon atom t o which the hydrogen is bonded. No allowance was made for scattering of the hydrogen atoms of the solvent molecule. The structure was refined by full-matrix leastsquares, minimizing the function Z z o ( ~ F o ~IFc1)2,where w = U ~ F ~ The / - ~carbon . and hydrogen atoms of each phenyl group were treated as a rigid body with D6h symmetry, c-c = 1.38 A and C-H = 0.96 A. The carbon and oxygen atoms of the phenyl groups and solvent molecule were refined with isotropic displacement parameters, and the remaining non-hydrogen atoms with anisotropic displacement parameters. The atomic scattering factors and anomalous dispersion corrections were taken from the International Tables for X - r a y Crystallograof the structure, involving 464 variables ~ h y The . ~refinement ~ and 14 765 reflections with Z > 3dI), converged a t R = 0.0405 and R, = 0.0429. The residual electron density showed no chemically significant features. The final atomic coordinates and atomic displacement parameters are listed in Table 3. AI1 calculations were performed using the GX program package.24 EHMO Calculations. These were carried out using the program CACAO. The geometry used was based on a planar D3h [Pt3(C0)6] unit with d(Pt-Pt) = 2.6 A and d(Pt-C) = 2.0 A. The [Re(C0)4]+unit was based on a n octahedral fragment with d(Pt-Re) = 2.7 A and d(Re-C) = 2.0 A.

3dZ)were used

Acknowledgment. We thank the NSERC (Canada) for financial support, SERC (U.K.) for an equipment grant, and the Iranian government for a studentship (to A.A.T.). Supporting Information Available: Tables giving H atom coordinates, anisotropic displacement parameters, and bond lengths and angles (6 pages). Ordering information is given on any current masthead page. OM9502852 (23)International Tables for X-ray Crystallography; Kynoch Press: Birmingham, U.K., 1974; Vol. IV. (24)Mallinson, P. R.; Muir, K. W. J . Appl. Crystallogr. 1985, 18, 51.